This study is ancillary to the Diet Intervention Study in Children (DISC), sponsored by the Division of Epidemiology and Clinical Applications, National Heart, Lung, and Blood Institute (NHLBI). DISC is a multicenter, randomized clinical trial designed to evaluate the feasibility safety and efficacy of a fat modified diet during adolescence to lower LDL-cholesterol. The NCI sponsored ancillary study will evaluate the effect of this fat modified diet on sex hormones during adolescence. The effect of the diet on total concentrations of hormones and bioavailable fractions of hormones will be determined. The NCI sponsored ancillary study will also identify characteristics of adolescents, including age, Tanner stage, anthropometric measures, physical activity and dietary intake that affect sex hormone levels and bioavailability of sex hormones. Dietary goals for the intervention group are to limit fat intake to 28% of calories and increase the ratio of polyunsaturated to saturated fats to approximately 1. Cholesterol intake will be restricted to 75mg/1000 calories. Children in the control group follow their usual diets. This study is being conducted collaboratively with scientists from the National Heart, Lung, and Blood Institute in Bethesda, MD; Children's Hospital in New Orleans, LA; the Johns Hopkins University in Baltimore, MD; the Kaiser Center for Health Research in Portland, OR; the Maryland Medical Research Institute in Baltimore, MD; the Medical College of New Jersey in Newark, NJ; Northwestern University in Chicago, IL; the University of Pittsburgh in Pittsburgh, PA; and the University of Iowa in Iowa City, IA.